Think about it this way, Amazon is customer-centric, so when it delivers search results it's implicitly saying "hey this is the relevant item at the best price per your search term". If it can't back that up then it'll often give a product substitute that is the best price.
IIRC, they got in trouble for this earlier this year for outright suppressing listings and had to back down a bit from this - instead of suppressing the listing wholesale you just get low traffic instead.